Various systems and facilities intake large quantities of water from various exposed natural and other above-ground water sources, such as rivers, lakes, oceans, reservoirs, irrigation and flood water canals, outdoor water parks, other water conveyance structures, and the like. Examples of such systems and facilities include hydroelectric plants, pulp and paper mills, steel mills, petro-chemical plants, municipal water systems and waste water plants, nuclear and other energy facilities that use the water for cooling or for other purposes, other water filtering or screening facilities or systems, etc. In all such systems it is important to screen naturally occurring debris found in the exposed above-ground water source from the flow of water that is taken into and employed by the system or facility. Such debris may include, for example, leaves, branches, and other portions of trees or other plants that have fallen into or grown in the water source, trash, and other debris that has been dumped or otherwise found its way into the exposed above-ground water source, etc. Such debris could cause significant damage to the system or facility obtaining water from the exposed above-ground water source if it were allowed to enter into the system or facility.
Various screening systems are known and used for preventing debris found in exposed above-ground water sources from entering into the systems or facilities described above. For example, fine mesh screening may be used to exclude even small pieces of debris from such systems. Screening systems with larger openings may be used, either alone or in combination with finer screening, to prevent large debris from entering the system or facility taking water from the exposed above-ground water source. Such larger opening screening systems may be used for preventing large debris from reaching finer mesh screening positioned downstream from the larger opening screening. Larger opening screening systems preferably do not dramatically adversely affect the water flow volume provided into the facility or system through the screening system.
An exemplary screening system of this type is known as an intake rack system or trash rack. Intake rack systems typically provide screening using a series of vertically oriented parallel blades or bars separated by spacers and mounted on horizontally oriented rods. The spacing between the blades forming the intake rack is selected to screen debris of the desired size from entering the water intake of the system or facility that the trash rack is protecting, without significantly reducing water flow into the water intake. Such intake racks may be made of metallic or non-metallic materials. Intake racks of this type are available, for example, from Hydro Component Systems, LLC of Watertown, Wis.
In a typical application, intake racks of this type may be mounted upstream from the water intake of a hydroelectric or other plant, system or facility that intakes water from a river or other similar exposed above-ground water source. The elongated vertically oriented parallel blades forming the intake rack extend downward into the water to prevent debris floating at the water surface or in the water below the water line from entering the system or facility. Various tools have been developed for cleaning accumulated debris from intake racks and similar screening systems. An example of such a tool is the Trash Rake System for Clearing Intake Racks and the Like described in U.S. patent application Ser. No. 11/144,393 filed on Jun. 3, 2005, the disclosure of which is incorporated herein by reference.
The leading edges of intake rack blades or bars, that is, the edges of the blades or bars that first contact water and debris flowing through and against the intake rack, may be formed to have curved edges. This has several advantages. Curved leading edges facilitate better water flow through the intake rack. Curved leading edges on the intake rack blades or bars also present less surface area over which a trash rake or other device must slide when cleaning debris from the intake rack. Less surface area means less friction, and less energy is thus required to move the trash rake or other device across the intake rack during a debris cleaning operation.
As mentioned above, intake rack systems may be made of metallic or non-metallic materials. For example, the vertical blades of an intake rack may be made of a durable plastic material, such as HDPE, or of a metal material, such as cold rolled steel.
Intake racks with metal rack blades or bars are the most commonly used. Such racks are very strong, and thus can withstand impacts from large debris and other incidental contacts without being seriously damaged in most cases. However, intake racks with rack blades made from metals, such as steel, also suffer from several significant limitations. Metal racks will rust unless treated with an epoxy coating. In cold weather the metal rack blades can conduct a freezing air temperature into the water, causing ice to form on the rack blades. This ice acts as an insulator, allowing the metal rack blades to conduct the cold temperatures deeper into the water to continue the freezing process. As ice forms on the rack blades in this manner the flow of water through the intake rack is restricted.
Plastic intake racks do not suffer from many of the limitations of metal racks. Plastic racks do not rust or corrode, and thus are the preferred solution for salt water applications in particular. Plastic racks don't transfer below freezing air temperatures into the water, and thus reduced water flow through the rack due to ice formation on the rack blades is eliminated. Marine growth, another potential cause of reduced water flow through an intake rack, also is less prevalent in plastic intake rack systems. Marine growth does not stick to plastic as well as it does to coated steel intake racks.
Given the many advantages of plastic intake racks, plastic racks are often a preferable solution. However, many facilities already have metal intake rack systems in place. To replace such installed metal rack systems with plastic racks would be an expensive undertaking.
What is desired is an intake rack system that combines the advantages of existing metal and plastic rack systems. What is desired, in particular, is an apparatus and method for bringing the advantages of plastic intake rack systems to existing metal rack system installations in an inexpensive manner that does not require removal, replacement, or reinstallation of the existing metal rack systems.